573  
FXUS02 KWBC 230700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 AM EST SAT FEB 23 2019  
 
VALID 12Z TUE FEB 26 2019 - 12Z SAT MAR 02 2019  
   
..PATTERN OVERVIEW
 
 
THE EXPECTED MEAN PATTERN AND EMBEDDED UNCERTAINTIES LOOK FAIRLY  
SIMILAR TO 24 HOURS AGO. A REX BLOCK CONFIGURATION SHOULD PERSIST  
OVER THE EAST-CENTRAL PACIFIC WITH A STRONG RIDGE/CLOSED HIGH  
MEANDERING OVER EASTERN ALASKA AND NORTHWESTERN CANADA WHILE  
FEATURES DROPPING INTO THE MID-LOW LATITUDE MEAN TROUGH PROGRESS  
TOWARD THE WEST COAST. IN THE MULTI-DAY MEAN PERSPECTIVE  
TELECONNECTIONS RELATIVE TO THE RIDGE'S POSITIVE HEIGHT ANOMALY  
CONTINUE TO FAVOR THE CONSENSUS IDEA OF A MODEST MEAN RIDGE CLOSE  
TO THE WEST COAST BY LATE PERIOD AND TROUGHING OVER EASTERN NORTH  
AMERICA. THERE ARE MULTIPLE SIGNIFICANT UNCERTAINTIES WITH  
EMBEDDED DETAILS THOUGH. THE MOST COMMON THEMES IN GUIDANCE  
CONTINUE TO BE THE POTENTIAL FOR SIGNIFICANT PRECIPITATION FROM  
THE CENTRAL AND NORTHERN WEST COAST INTO THE NORTHERN ROCKIES AND  
PERSISTENCE OF VERY COLD TEMPERATURES OVER AND NEAR THE NORTHERN  
HALF OF THE PLAINS. THERE WILL LIKELY BE MULTIPLE PRECIPITATION  
AREAS OVER THE EASTERN HALF OF THE COUNTRY DURING THE TUE-SAT  
PERIOD BUT SPECIFICS WILL BE SENSITIVE TO THE UNCERTAIN DETAILS AT  
THE SURFACE AND ALOFT.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
THE DIFFICULTY THAT AN UPPER HIGH OVER THE NORTHEASTERN  
PACIFIC/NORTHWESTERN NORTH AMERICA TENDS TO CREATE FOR THE  
FORECAST IS EVIDENT AGAIN TODAY, WITH SIGNIFICANT SPREAD QUICKLY  
DEVELOPING FOR FEATURES TO THE SOUTH AND SOUTHEAST OF THE HIGH.  
ALREADY FROM VERY EARLY IN THE PERIOD THERE ARE MEANINGFUL  
DIFFERENCES FOR FLOW DETAILS OVER AND OFFSHORE THE PACIFIC  
NORTHWEST AS WELL AS FOR DOWNSTREAM FLOW OVER THE NORTHERN  
U.S./SOUTHERN CANADA. REGARDING THE FORMER, THERE IS AGREEMENT IN  
PRINCIPLE THAT INITIAL ENERGY SHOULD CLOSE AN UPPER LOW WHILE  
MID-LATITUDE ENERGY APPROACHING FROM THE WEST IS INCORPORATED INTO  
THE SOUTHERN SIDE OF THE CIRCULATION BY DAY 4 WED. HOWEVER THERE  
ARE SIGNIFICANT POSITION DIFFERENCES FOR THIS UPPER LOW AS OF  
EARLY WED WITH FURTHER DIVERGENCE THEREAFTER. LATEST GFS RUNS  
INCLUDING THE 00Z VERSION ARE PARTICULARLY FAST WITH THIS SYSTEM  
VERSUS MOST OTHER GUIDANCE, ULTIMATELY LEADING TO ANOTHER VERY  
DEEP GREAT LAKES STORM BY SAT. THE 18Z FV3 GFS CLUSTERS TOWARD  
THE OTHER SLOWER SOLUTIONS. OVERALL PREFERENCE LEANS INCREASINGLY  
AWAY FROM THE GFS BY MID-LATE PERIOD. MEANWHILE OUT-OF-SYNC  
SHORTWAVE DETAILS FROM THE NORTHERN PLAINS EASTWARD (WITH  
SUFFICIENTLY SMALL SCALE LEADING TO FAIRLY LOW PREDICTABILITY)  
AFFECT POSSIBLE SURFACE WAVINESS AND SNOWFALL AMOUNTS/COVERAGE.  
THE GFS CONTINUES TO BE ON THE STRONG SIDE OF THE FULL SPREAD WITH  
ANY LOW PRESSURE WHILE ECMWF/ECMWF MEAN RUNS PERSIST WITH NO  
REFLECTION AT ALL. TAKEN AS A WHOLE THERE SEEMS TO BE MORE  
POTENTIAL FOR MODEST WAVINESS THAN INDICATED BY THE ECMWF SCENARIO  
BUT IT SHOULD BE WEAKER THAN IN THE GFS--FAVORING AN INTERMEDIATE  
SOLUTION.  
 
LATER IN THE PERIOD THERE IS A REASONABLE DEGREE OF  
PERSISTENCE--THOUGH WITH A SOMEWHAT SLOWER TREND--FOR THE SYSTEM  
LIKELY TO TRACK TOWARD THE WEST COAST. THIS SLOWER TREND ARGUES  
FOR AT LEAST INTERMEDIATE TIMING BETWEEN THE FASTER 12Z  
ECMWF-ECMWF MEAN/18Z FV3 GFS AND OTHER SOMEWHAT SLOWER SOLUTIONS.  
BY SAT ECMWF/ECMWF MEAN SCENARIO OF KEEPING THE EARLY PERIOD UPPER  
LOW OFFSHORE VANCOUVER ISLAND WOULD LEAD TO SOME INFLUENCE ON THE  
SYSTEM WHILE OTHER GUIDANCE SHOWS INLAND EJECTION ALBEIT SLOWER  
THAN IN THE GFS. FARTHER EAST ONE NOTABLE DIVERGENCE IS FOR THE  
PATH OF A SOUTHERN CANADA UPPER LOW, FOR WHICH GFS RUNS LEAN TO  
THE SOUTHERN PART OF THE SPREAD. EVEN IF THE SEQUENCE OF EVENTS  
LEADING TO THE DEEP EASTERN STORM BY NEXT SAT CURRENTLY LOOKS  
QUESTIONABLE, THERE IS A SIGNAL FOR SOME AMOUNT OF SURFACE  
DEVELOPMENT (SUCH AS IN THE PAST TWO ECMWF RUNS AND 12Z/18Z GEFS  
MEANS. ALBEIT WITH VERY UNCERTAIN LATITUDE THERE IS SOMEWHAT MORE  
AGREEMENT TOWARD THE IDEA OF LOW PRESSURE JUST OFF THE EAST COAST  
DURING THE DAY SAT AS HEIGHT FALLS ALOFT APPROACH.  
 
THE UPDATED FORECAST STARTS WITH A MULTI-MODEL (18Z GFS/FV3 GFS  
AND 12Z ECMWF/UKMET/CMC) BLEND DURING THE FIRST HALF OF THE PERIOD  
TO REFLECT A CONSENSUS OR INTERMEDIATE SOLUTION AS APPROPRIATE FOR  
INDIVIDUAL FEATURES EARLY IN THE PERIOD. BY MID-LATE PERIOD THE  
FORECAST INCLUDES 30-60 PERCENT TOTAL INPUT OF THE 18Z GEFS/12Z  
ECMWF MEANS, WITH SOME IDEAS FROM THE 12Z ECMWF/CMC AND 18Z FV3  
GFS FOR LOCALIZED DETAIL.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
OVER THE WEST SOME OF THE DAY-TO-DAY DETAILS HAVE VARIED BUT  
GUIDANCE IS CONSISTENT IN PRINCIPLE WITH THE POTENTIAL FOR  
SIGNIFICANT PRECIPITATION--IN THE FORM OF RAIN AND HIGHER  
ELEVATION SNOW--FROM THE CENTRAL/NORTHERN WEST COAST INTO THE  
NORTHERN ROCKIES. THERE MAY BE A BRIEF BREAK IN ACTIVITY AROUND  
LATE WEEK BETWEEN INITIAL MOISTURE FLOW AND THE ARRIVAL OF ANOTHER  
SYSTEM BY SAT. BEST PROBABILITY FOR HIGHEST 5-DAY TOTALS STILL  
COVERS NORTHERN CALIFORNIA/SIERRA NEVADA RANGE AND SOUTHWESTERN  
OREGON WITH AT LEAST 5-10 INCHES LIQUID POSSIBLE AT SOME  
LOCATIONS. EXPECT MEANINGFUL BUT SOMEWHAT LOWER MAX TOTALS OVER  
THE NORTHERN ROCKIES.  
 
PRECIPITATION COVERAGE AND INTENSITY FROM THE PLAINS TO EAST COAST  
CONTINUE TO BE DIFFICULT TO PINPOINT DUE TO SIGNIFICANT  
DIFFERENCES IN SHORTWAVE ENERGY AND SURFACE EVOLUTION. FROM TUE  
INTO WED NIGHT AN AREA OF MOSTLY LIGHT SNOW MAY PROGRESS EASTWARD  
FROM THE PLAINS. MEANWHILE SOUTHERN STREAM IMPULSES MAY PROMOTE  
PERIODS OF RAINFALL ACROSS THE GULF COAST STATES OVER THE COURSE  
OF THE PERIOD. TOWARD FRI-SAT THERE MAY BE AN EXPANSION OF  
PRECIPITATION COVERAGE OVER THE EASTERN STATES (SNOW NORTH AND  
RAIN SOUTH) IN ASSOCIATION WITH SOME DEGREE OF SURFACE DEVELOPMENT  
OVER THE EAST AND/OR EXTREME WESTERN ATLANTIC.  
 
WITHIN THE AREA OF MUCH BELOW NORMAL TEMPERATURES CENTERED OVER  
THE NORTHERN HALF OF THE PLAINS, COLDEST ANOMALIES (AT LEAST 30F  
BELOW NORMAL AT SOME LOCATIONS) SHOULD EXIST EARLY AND LATE IN THE  
PERIOD. SOME OF THE COLD AIR WILL EXTEND EASTWARD EARLY-MID  
PERIOD FOLLOWED BY A MODERATING TREND. FLOW FROM THE PACIFIC WILL  
KEEP MORNING LOWS ABOVE NORMAL OVER ALL BUT THE EXTREME NORTHERN  
PARTS OF THE WEST, AS WELL AS OVER THE SOUTHERN TIER, WHILE CLOUDS  
AND PRECIPITATION WILL TEND TO KEEP HIGHS CLOSER TO NORMAL.  
 
RAUSCH  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION AND WINTER WEATHER OUTLOOK  
PROBABILITIES ARE FOUND AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
 

 
 
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